One of the players had expanded well and was in the position of having 5 settlements and 1 city. The Barbarians attacked, we lost and said player had to downgrade their city to a settlement but had no further settlement pieces available.

Should they have to remove the settlement altogether (which seems rather harsh) or should they remove another settlement to replace it (also a loss of 2VP)? We settled on letting the player use a ship to represent the settlement until one was upgraded to a City.

However the question still remains. The player potentially gained an advantage by building a settlement when he should have built a knight to protect himself, so perhaps he should lose both the city and settlement? If you do remove both it could potentially leave the player with, quite literally, "a road to nowhere", i.e. a road not connected to anything. It could also open up previously closed routes for other players and completely change the game.If we proceed with using a ship as a temporary settlement should the player be forced to upgrade a settlement to a city as their next move?